Electric valve protective system



06L 1933- s. WIDMER E AL 2,132,839

ELECTRIC VALVE PROTECTIVE SYSTEM Filed March 5, 19154 3 Sheets-Sheet l Oct. 11, 1938. S. WIDMER Er AL 2,132,839

ELECTRIC VALVE PROTECTIVE SYSTEM Filed March 5, 1934 5 Sheets-Sheet 2 AAAAA] Oct. 11, 1938. s. WIDMEIR ET AL 2,132,839

ELECTRIC VALVE PROTECTIVE SYSTEM Filed March 5, 1954 3 Sheets-Sheet 3 will J UNITED STATES PATENT OFFICE 2,132,839 s scrmc VALVE rnorscrrva SYSTEM Stefan Widmer and Max Hiirlimann, Baden, Switzerland, assignors to Aktlengesellscliaft Brown Boveri & Cie., Baden, Switzerland, a joint-stock company of Switzerland Application March 5, 1934, Serial No. 714,107 In Germany-March 4, 1933 \y 19 Claims. (Cl. 175-363) (Granted under the provisions of sec. 14, act of March 2, 1927; 357 0. G.

This invention relates in general to improvein the voltage of a circuit associated with the merits in electric valve protective systems and valve. v more particularly to static means for causing Another object of the present invention is to interruption of the flow of current through the provide a protective system for an electric valve, electric valves upon occurrence of a disturbance which system is responsive to the Occurrence of 6 in the circuits thereof. an incipient sudden discharge of a capacitor Electric valves may be utilized in combination connected with the circuits of the valve.

with suitable apparatus and circuits to form Objects and advantages other than those above systems such as alternating current rectifying, described will be apparent from the following de- 10 direct current inverting, frequency converting, se pti n When d in c nec n w th e 8 direct current voltage converting, or current incompanying drawings, in which: terrupting systems. The flow oi current may Fig. l diagrammatically illustrates one embodibe controlled and regulated by suitable energiza ment of the present invention applied to the tion of discharge controlling means such as concontrol of an alternating current rectifier and lo trol electrodes. Upon occurrence of a disturb respo s ve to the diffe c between t Voltage i" ance in any such system, the flow of cu re t is or" the rectifier output circuit and the terminal most conveniently interrupted by energizing Voltage of a Capacitor Conneeted therewith; suitable control electrodes of the valve negative Fi 2 dia rammatically illustrates a portion 13/ with respect to the cathode thereof. such of a modified embodiment of the present invenenergization was obtained heretofore by means ti n difiering o the embodiment illustrated of mechanical devices which required an apprein Fig. l n tha the protective Circuits are ciablc length of time for their operation where pon ve to h rate f fl w of u r n hr u as it is desirable to cause interruption of the flow the capacitflli of fault current within the shortest possible time g- 3 di ma i a y u t s a portion of to P v nt damage to the valve and to th ap another modified embodiment of the present in- 25 paratus connected therewith. It is, therefore, Vention differing from embodiment 111115- preferable to utilize static means such as auxeed n g- 2 n t means a p fl for iliary electric valves which do not introduce an sulating the output voltage of the rectifier; appreciable time delay in the operation of the and protective circuits. When the valve supplies cur- 4 d ag a a y illustrates another 30.

rent to a direct current output line, the operamodified embodiment of the present invention in tion of the protective circuits is preferably,ini- W i -h the e c tat System therectifiel is tiated in response to the voltage or the current utilized as a source of current for the control of a capacitor connected with the direct current electrode I line whereby the action of the protective mem- R ferring more particularly to the drawings b 35 bers may be initiated before the disturbanc ha characters of reference, reference numeral 6 reached its full efiect. designates an alternating current supply line It is, therefore, one of the objects of the pres herein represented as a three. phase lin A dient invention to provide a protective system for root Current e av g a neg Condufiiiol' 44) an electric valve in which the flow of current in 7 and & DOSiliil/e @Qnductol 3 is cinnected with the valve is interrupted by the action of static it ble cur nt consuming d vic s shown) means only. which in the embochment illustrated in Fig, 1

Another object or the present invention is to are a sumed o be n pa l f r rning ener provide a protective system for an electric val to the line upon sudden decrease of the voltage 45 for interrupting the flow of fault current thlflllgh thereof. Line i, 3 receives current from line 6 45 the valve before such current has reached its thr u h n electric translation y m mprisfull intensity. ing a transformer l2 having a primary winding Another object of the present invention is to H Connected, t a c i a e o b provide a protective system for an electric valve mentioned heleinaffier, with line 5 and a by which the how of current through the valve ondary winding 13, and through an electric valve 59 may be temporarily interrupted upon occun'encg I6. Valve 18 is assumed to be of the vapor type of a disturbance. having a cathode I! connected with conductor Another object of the present invention is to 8 but it will be understood that the present inv provide a protective system for an electric valve, vention is also applicable to the control of valves 5 which system is responsive to sudden variations of other types. The valve is provided with suit- 5 able discharge igniting and maintaining means which are, well known; the choice of any particular type of such means does not affect the operation of the embodiment illustrated in Fig. 1 and the means are, therefore, not shown in such figure.

Winding l3 comprises a plurality of phase displaced portions which may be connected in star to form a neutral point connected with conductor l and which are severally connected with the anodes as at it of valve it. The how of current through each anode of the valve is controlled by means of a control electrode such as at l8 energized by means to be described hereinafter. In the description of the several embodiments of the present invention the potential of cathode M will be taken as datum for the potentials of the several control electrodes of the valve and consequently any electromotive force or potential difierence impressed between the cathode and the control electrode is equal in value to the potential ofsuch control electrode. In a similar manner the potentials of the oathodes of any aumliary valves utilized, in the system will be used as datum for the potentials im-' pressed on the associated control electrodes.

In the embodiment illustrated in Fig. 1, the control electrodes 83 of valve it are not utilized for regulating the output voltage of the valve during normal operation thereof and may, there'- fore, remain entirely unenergized during such operation. As is well known, however, to insure the normal flow of current through the valve without disturbances such as extinctionof the discharge or failure of one or more anodes to carry current, it is preferable to energize the control electrodes from a source of positive potential such as a battery I9 through a current limiting resitor 2| and separate control electrode resistors as at 22. To cause interruption of the flow of current through valve it, a source of negative potential such as a battery 23 is provided, the battery having an intermediate point thereof connected with the cathode 23 of an auxiliary valve 24, common to the entire system, having an anode 26 and a control electrode 21. Valve 24 is preferablyof the vapor type and the operation of such valve and of the system will vbe described accordingly although it will be understood that other types of valves may be used even though resulting in a somewha ..modified method of operation.

The negative terminal of-battery 23 is connected with conductor I through a rheostat 3| and a capacitor 32, the point of junction between the rheostat and the capacitor being connected with control electrode 21 through the usual current limiting resistor 23. Anode 26 is connected with the junction point of resistors 2| and 22, such connection including the contacts 33 of a time delay relay 34 when valve 24 is of the vapor type. The coil of relay 34 is energized from a current transformer 36 inserted in the connection between winding .H and line 3 to cause delayed opening of contacts 33 in response to flow of excessive current through current transformer 36. Winding H is connected with line 3 through a circuit breaker 3'! provided with comparatively slow acting tripping means.

In operation, the system being connected as shownand line 3 being energized, upon closure of circuit breaker 31 the anodes of valve l6 receive phase displaced alternating voltages from winding i3 as is well known in the art. Con= trol electrode 29 receives a negative potential aiaassa from battery 23 through rheostat 3|, thereby preventing the flow of current through valve 24 from batteries 23 and IS. The control electrodes of valve it therefore receive only a positive potential from battery l9 and insure a normal flow of current through the valve, such current being delivered to line 7!, 8 at a voltage depending on the construction of transformer i 2. Capacitor 32 being connected across line i, 3 is charged at a portion of such voltage equal to the voltage of line i, 8 minus the voltage of battery 23. The terminal voltage of capacitor 32 follows the gradual variations of the voltage of line i, 8 resulting from the changes of load connected with line i, 3 or from changes in the voltage of line 3; such changes result in a comparatively small flow of charging current through rheostat 38, causing an inappreciable voltage drop through such rheostat.

Upon occurrence of a disturbance such as a short circuit in line i, 8 or a backfire" within valve 113 the voltage of line 1, 3 suddenly collapses. Decrease of the voltage of line i, 8 is, however, not immediately followed by a corresponding decrease in the voltage of capacitor 32 occurs before the fault current has reached the full value thereof resulting in the complete collapse of the' line voltage. Valve 24 having become conductive, the control electrodes of valve l3 receive, from battery 23, a negative potential which overcomes the positive potential of battem is. The anodes of the valve, with the exception of the anode carryingcurrent at time considered therefore become inoperative and the flow of current through valve i6;ceases when the current through the operating anode falls to zero. The flow of current through valve is is therefore interrupted in a fraction of one cycle of the voltage in line 6 whereas such interruption would take considerably longer time by the use of mechanical means.

Following the sudden decrease in the voltage of line ,1, Q capacitor 32 slowly discharges either through the backflring arc in valve IE or through by elimination of the faulty portion of the line, I

capacitor 32 continues to discharge through the load connected with line I, 8 at a rate depending mainly upon the adjustment of-rheostat 3|. After a period of time depending upon such adjustment the potential impressed on the control electrode 21 by capacitor 32 is again overcome by the potential of battery 23 and control electrode 21 is again negative. Valve 24 being of the vapor type, however, control electrode 21 is generally incapable of interrupting the discharge therethrough. Relay 34 is accordingly so adjusted that such relay will open the circuit of valve 24 after a sufficient length of time following initiation of the disturbance to first permit control electrode 21 to again become negative. Upon opening of contacts 33 the flow of current through valve 24 ceases and control electrode 28 regains control to prevent reestablishment of such flow of current. The, valve l8 is thus returned to the normal operating condition thereof and the normal flow of current therethrough is automatically reestablished. If the control electrodes fail to interrupt the flow of current through the valve for any reason such as a defect in the system, circuit breaker 31 interrupts the flow of current after a predetermined time delay.

In the above described system, therefore, battery l9 constitutes means for impressing, on the control electrodes of valve l8, potential of sign and magnitude operative to insure a normal flow of current between lines 8 and 1, 8 by way of valve l6. Auxiliary valve 24 is operable to connect the source of negative potential 23 with the control electrodes, the control electrode 21 of valve 24 receiving from battery 23 potential of sign and magnitude operative to normally maintain valve 24 non-conductive. Capacitor 32 is connected across line 1, 8 to be charged therefrom at a predetermined portion of the voltage thereof and is connected with control electrode 21 to make valve 24 conductive upon occurrence of a disturbance causing a sudden decrease in the voltage of line 1, 8 and consequently upon suddenly occurring difference between the voltage of capacitor 32 and the quantity voltage of line 1, 8 less the voltage of battery 23. Valve 24 constitutes static means responsive to sudden variation of the voltage impressed on capacitor 32 from line 1, 8 for temporarily maintaining the control electrodes of valve l8 at potential of sign and magnitude operative to cause interruption of the flow of current through valve i6. Relay 34 constitutes time delay means responsive to the occurrence of the disturbance for momentarily opening the circuit of valve 24 whereby such valve returns to the non-conductive condition.

, In the modified embodiment illustrated in Fig. 2, capacitor 32 is connected across line 1, 8 through rheostat 3| to be charged at the full line voltage. Control electrode 21 is connected with battery 23 through resistor 28 and the secondary winding of a current transformer 38 inserted between rheostat 3| and conductor 3, such connection including a voltage divider 43 if so desired.

In the present embodiment; when circuit breaker 31 is closed to cause the supply of current to line 1, 8 from line 8, control electrode 21 is again maintained at a negative potential from battery 23. Valve 5 then supplies current to line 1, 8 at the operating voltage thereof. Such voltage is suddenly impressed on capacitor 32 and rheostat 3|, and capacitor 32 is charged at a rate depending upon the value of rheostat 3|, the charging current of the capacitor increasing at first to afterwards decrease to zero when the charge of the capacitor is complete. The voltage appearing at the terminals of the secondary winding of the current transformer 38 is proportional to the rate of change of flow of such charging current and such voltage accordingly presents a negative half wave followed by a positive half wave of lesser magnitude, the ratio of the magnitudes of such half waves depending upon the value of rheostat 3|. The negative half wave is without effect on control electrode 21 which is already negatively energized from battery 23 and rheostat 3| and voltage divider 43 1 are so adjusted that the following positive half wave is of insuilicient magnitude for overcoming the negative voltage of battery 23. Valve 24 therefore remains non-conductive during the establishment of the flow of ,current through valve l6.

Upon occurrence of a disturbance such as a short circuit or backfire, the voltage of line 1, 8 suddenly decreases to a very low value and capacitor 32 suddenly begins to discharge through the point of fault or through the backfiring arc. The discharge current of capacitor 32 at first increases in value and thereafter decreases to zero when the discharge of the capacitor is complete. Current transformer 38 accordingly impresses, on control electrode 21, a positive half wave followed by a negative half wave of lesser magnitude, the positive half wave being of sufficient magnitude to overcome the potential of battery 23 and bring control electrode 21 to a positive potential releasing the flow of current through valve 24. The action of valve 24 in causing interruption of the flow of current through valve I8 is then similar to that explained above with respect to Fig. l and valve 24 is returned to the non-conductive position by opening of relay 34 following the return of control electrode 21 to a negative potential.

In the present embodiment therefore current transformer 38 and valve 24 operate in response to a sudden decrease in the voltage of line 1, 8 and are directly responsive to the occurrence of an incipient sudden discharge of capacitor 32 to cause the impression of the negative potential of battery 23 on the control electrodes of valve Hi.

In the embodiment illustrated in Fig. 3, battery 23 is continuously connected with the control electrodes l8 through separate serial pairs of resistors as at 2| and 22. The control electrodes are also sequentially connected with battery l9 through a distributor 39 having a brush connected with cathode 28, anode 26 being connected with the positive terminal of battery I9. The

brush of distributor 39 is actuated in relation with the voltage cycle of line 6 by suitable means such as a synchronous motor 4| energized from line B or from winding l3 and provided with suitable starting and synchronizing means (not shown). The segments of distributor 39 are preferably of such width that the flow of current through valve 24 is interrupted upon movement of the brush from one segment to the next over the intervening insulation. The timing of the energization of the several control electrodes in the cycle may be adjusted bymeans of a lever 42. In the present embodiment the connections of current transformer 38 with cathode 28 and control electrode, 21 are reversed and comprise a source of positive bias potential'such as a battery 43.

Upon closure of circuit breaker 31, motor 4| is started and brought to'synchronous operating speed as is well known in the art. The control electrodes of valve l8 are generally maintained at a negative potential from battery 23 and are sequentially brought to a positive potential from battery is through valve which is maintained in the conductive condition by energization of control electrode 21 at the potential of battery 43. The flow of current through valve I8 is accordingly established at a voltage depending upon the adjustment of lever 42. Upon impression of such voltage on line 1, 8, capacitor 32 is suddenly charged, the flow of charging current causing current transformer 38 to impress on control electrode 21 a positive half wave assisting the action of battery 43 followed by a negative half wave of lesser magnitude insufiicient to offset the action of battery 43. The operation of valve it therefore continues, such action being regulated by manual or automatic adjustment of lever 42.

Upon occurrence of a short circuit or of a backfire, capacitor 32 suddenly discharges, the discharge thereof, when in the incipient stage, causing current transformer 38 to impress on control electrode 2! a negative half wave overcoming the action of battery 43 followed by a positive half wave of lesser magnitude at the final stage of the discharge. voltage divider 40 are so adjusted that such negative half wave remains at a magnitude greater than the voltage of battery 43 over a time interval during which the brush of distributor 39 moves over several segments of the distributor. Such movement of the brush causes the current through valve 26 to be interrupted and control electrode 21 can, therefore, regain control to prevent further flow of current through valve 24. The connection between battery l9 and distributor 39 remains interrupted during a period of time sufiicient to cause the flow of current through valve It to be interrupted as a result of the energization of the control electrodes of valve Hi from battery 23 only. When the voltage of battery 43 is no longer overcome by the voltage of current transformer 38, valve 24 again becomes conductive and the normal operative condition of valve is is reestablished.

In the present embodiment therefore battery 23 is a source of negative potential connected with cathode ll and the control electrode 98. Battery 19 is a source of positive potential connected with cathode ii and cooperating with valve 26 and distributor 39 for sequentially impressing on the control electrodes of valve 56 potential overcoming the potential of battery 23 and of such sign and magnitude as to be operative to release the flow of current through the anodes of the valve. Battery 43, impresses on control electrodes 27, potential of sign and magnitude operative to normally maintain valve 24 conductive while current transformer 38, voltage divider 40 and rheostat 3! connect control electrode 21 with capacltor32 whereby valve 24 is temporarily made non-conductive and temporarily interrupts the connection between battery I9 and the control electrodes of valve l6 upon other generating or converting means. Battery i9 is omitted and the control electrodes of valve 16 receive alternating voltages from an excitation' transformer-'44 supplying current to the excitation anodes' 46 of valve 16 through resistors .41 .and a reactor 45. Each control electrode is connected with the proper terminal of trans-. former 44 tov obtain positive energization of the control electrode when the flow of current is to occur through the associated anode. Control electrode I8 only is shown connected with anode 26 through resistor 22, .each of the control electrodes being similarlyconnected with additional auxiliary valves having the cathodes and the Rheostat 3i and aisaesa control electrodes thereof provided with common.

connections. The cathodes of the auxiliary valves are connected with the movable tap of a voltage divider 48 connected between-the neutral point of winding 13 and cathode ll, and are also connected with one terminal of a capacitor 29 connected with cathode ii. Capacitor 32 is connected with the neutral point of winding 43 and with the tap of a second voltage divider connected in parallel with voltage divider 48. The tap of voltage divider 5! is connected with the control electrodes of the auxiliary valves through a rectifying device at and, if so desired, through a negative bias battery ti. Device 56 is preferably bridged by a resistor 58 of high resistance value. A third voltage divider 53 is connectedbetween cathode ll and with the portion of conductor 1 comprised between the reactor 52 and the load, the negative portion of such voltage divider being bridged by another capacitor 54 connected with the control electrodes of the auxiliary valves through a second rectifying device till, a second resistor 59 and battery iii. The connection between cathode ill and conductor 8 preferably includes a circuit breaker 62 arranged to be opened upon flow therethrough of a current of any magnitude from conductor 8 to cathode li. Circuitbreaker 62 may be caused to automatically reclose in re sponse to the voltage between conductor 8 and cathode ll by means of a connection therebetween comprising the closing coil of the circuit breaker and a closing switch 53.

In operation, upon closure of circuit breaker 37, a discharge being already ignited in valve It by the igniting means (not shown) and main- 1 tained by means of transformer 44 and anodes 36, the flow of currrent through the anodes of valve it may occur and is insured by the energization of the control electrodes of the valve from transformer 66. The auxiliary valves are all non-conductive as a result of the negative energization of the control electrodes thereof from battery ti. The normal operating output voltage of valve 86 is impressed on the closing coil circuit of circuit breaker 62 and such circuit breaker closes to complete the connection of line i, 8 through valve i5. Capacitors 32, 49 and 54 are gradually charged through the associated voltage dividers; the taps of the voltage dividers are. so adjusted that the potential impressed on the control electrodes of the auxiliary valves is slightly negative, irrespective of alternating voltages appearing at the terminals .of reactor 52 as the result of the flow therethrough of alternating components of the current in line 1, 8.

. Upon occurrence of-a short circuit in line I, 8,

the voltage in such-line collapses but the volt- 'age across voltage divider 48 is momentarily maintained at substantially operating value by the action of reactor 52. As a result of the short circuit, the negative terminal of capacitor 54 is operatively connected with the positive terminal of capacitor 49 and the positive terminal of capacitor 54 impresses, on the control electrodes 21 through device 51, a positive potential overcoming the negative potential of battery 5|. The auxiliary valves are thus made conductive and cause impression of the negative potential of the negative-terminal of capacitor 49 on the control electrodes l8 of valve IS. The flow of current through valve I6 is accordingly inter rupted; During such operation, the tap of voltage divider Si is maintained at a lower potential than the, tap of voltage divider 53 but a discharge of capacitor 54 into capacitor 32 is prevented by rectifying device 56. Upon interruption of the flow of current through valve l6 and removal of the short circuit fault by suitable means, the capacitors are gradually recharged at their normal voltages by the generators con-. nected with line 1, 8 whereby the control electrodes 21 are again made negative. Each auxiliary valve being connected with a source of alternating current; that is, transformer 44, the flow of current therethrough passes through zero once per cycle and remains interrupted upon negative energization of the control electrodes to thereby reestablish the normal operation condition of valve is. Even if no generator were connected with line 1, 8, upon complete discharge of capacitors 32, 54 and 49, the control electrodes of the auxiliary valves would return to a negative potential from battery 6|. Resistors 58 and 59 are provided to complete the connection of capacitors 32 and 54 with the control electrodes of the auxiliary valves during normal operation thereof, an operative connection not being then provided by rectifying'devices 56 and 51.

Upon occurrence of a backfire in valve [5, the voltage between the neutral point of winding l3 and cathode i7 collapses whereas the voltage between conductors 1 and 8 is momentarily maintained by the action of reactor 52. Capacitor 32 then provides the positive potential for the control electrodes of the auxiliary valves and the interrupting operation occurs in a manner similar to that eirplained above. The flow of reverse current through valve l6, which cannot be interrupted by the control electrodes, is interrupted by opening of circuit breaker 52. Upon subsequent return-of the auxiliary valves to the non-conductive condition, valve l6 returns to the normal operating condition thereof and circuit .breaker 62 automatically reconnects cathode I! with conductor 8.

In the present embodiment, capacitor 49 accordingly constitutes a source of negative potential connected with cathode i1 and connected to be charged from line 1, 8 at a predetermined portion of the voltage thereof. Capacitors 32 and 54 then normally impress on the control electrodes 21 a potential lower than the potential of the cathodes 28 whereby the valves 24 cause the control electrodes i8 to receive temporarily from capacitor 49 a negative potential upon sudden decrease of the voltage of line 1, 8.

Although but a few embodiments of the present invention have been illustrated and described, it will be apparent to those skilled in the art that various changes andmodiflcations may be made therein without departing from the spirit of the invention or from the scope of the appended claims.

It is claimed and desired to secure by Letters Patent:

1. In a system for controlling the flow of elec-v tric current, an electric current supply circuit, electric translation means connected with said circuit and comprising an electric valve having an anode with an associated control electrode and a cathode, an electric current output circuit connected with said translation means, and static means responsive to a sudden decrease only in the voltage of said output circuit for impressing on said control electrode a potential of" sign and magnitude operative to cause interruption of the flow of current through said valve.

2. In a system for controlling the flow ofelectric current, an electric current supply circuit,

5 electric translation means connected with said circuit and comprising an electricvalve having an anode with an associated control electrode and a cathode, an electric current output circuit connected with said translation means, means for impressing on said control electrode potential of sign and magnitude operative to insure a normal flow of current between said circuits by way of said valve, and static means responsive to a sudden decrease only in the voltage of said output circuit for impressing on said control electrode a potential of sign and magnitude operative to cause interruption ofthe'flow of current through said valve.

3. In a system for controlling the flow of electric current, an alternating current supply line, an electric valve connected with said line and having ananode with an associated control electrode and a cathode, a line connected with said valve, and static means responsive to a sudden decrease only in the voltage of said output line for impressing on said control electrode a potential of sign and magnitude operative to cause interruption of the flow of current through said valve.

4. In a system for controlling the flow of electric current, an alternating current supply line, an electric valve connected with said line and having an anode with an associated control electrode and a cathode, a direct current output line connected with said valve, means for impressing on said control electrode potential of sign and magnitude operative to insure anormal flow of current between said lines. by way of said valve, and static means responsive to a direct current output sudden decrease only in the voltage of said out- 7 put line for impressing on said control electrode a potential of sign and magnitude operative to cause interruption of the flow of current through said valve.

5. In a system for controlling the flow of electric current, an alternating current supply line, an electric valve connected with said line and having an anode with an associatedcontrol electrode and a cathode, a direct current output line connected with said valve, a capacitor connected to be charged from said direct current line, and static means responsive only to sud- .den discharge of said capacitor into said direct current line for impressing on said control electrode a potential of sign and magnitude operative to cause interruption of the flow of current through said valve. I

a 6. In a system for controlling the flow of electric current, an alternating current supply line, an electric valve connected with said line and having an anode with an associated control electrode and a cathode, a direct current output line connected with said valve, a capacitor connected across said direct current line to be charged therefrom, a source of negative potential connected with said cathode, an auxiliary valve operable to connect said source with said control an electric valve connected with said line and having an anode with an associated control electrode and a cathode, a direct current output line connected with said valve, a capacitor connected across said direct current line to be charged therefrom, a source of negative potential connected with said cathode, an auxiliary valve operable to connect said source with said control electrode, a control electrode for controlling the action of said auxiliary valve, means for impressing on the second said control electrode potential of sign and magnitude operative to nolly maintain said auxiliary valve nonconductive, and means for connectimgathe secend said control electrode with said capacitor whereby the second said valve is de conductive upon sudden decrease of the voltage of said direct current line resulting from a disturbance in the system, and time delay means responsive to the occurrence of" the disturbance to momentarily open the circuit of the second said valve whereby the escond said valvereturns to the non-conductive condition. y

8. In a system for controlling the flow of elec tric current, an alternating current supply line,

control electrode, a control electrode for controlling the action of said auxiliary valve, means for impressing on the second said control electrode potential of sign and magnitude operative to normally maintain said aumliary valve non- 9. In a system for contro the flow of electric current, an alternating current supply line,

an electric valve connected with said line and having an anode with "an associated control electrode and a cathode, a direct current output line, connected with said valve, a capacitor connected across said direct current line to be charged therefrom, a source of negative potential connected with said cathoda'an auxiliary valve operable to connect said source withsaid control electrode; a control electrode for controlling the action of said auxiliary valve, means for impressing on the second said control electrode potential of sign and magnitude operative to normally maintainsaid auxiliary valve non-conductive, means for connecting. the second said control electrode with said capacitorwhereby the second said valve is made conductive .upon the occurrence of an incipient sudden discharge 0! said capacitor through said direct current line resulting from a disturbance in the system, and time delay means responsive to the occurrence of the disturbance to momentarily open the circuit of the second said valve whereby the second said valve returns to the non-conductive condition. s v

10. In a system for controlling the flow of and having an anode'wlth an associated control electrode ands. cathode, a direct current output aisaeso having an anode connected with said control electrode and having a control electrode and a cathode connected with said capacitor, a second capacitor connected with said direct current line and with the second said control electrode to impress thereon potential from said direct cur rent line lower than the potential of the second said cathode whereby the second valve causes the first said control electrode to temporarily receive a negative potential from the first said capacitor upon sudden decrease in the voltage of said direct current line.

ll. In a, system for controlling the flow of electric current, an alternating current supply line, an electric valve connected with said line and having an anode with an associated control electrode and a cathode, a direct current output line connected with said valve, a source of negaof positive potential connected with said cathode,

means for intermittently connecting the second said source with said control electrode to overcome the action of the first said source, and means responsiveto a sudden decrease only in the voltage of said output line for temporarily preventing the said connection of the second said source with said control electrode.

12. In a system for controlling the fiow of electric current, an alternating current supply line, an electric valve connected with said line and hav'mg an anode with an associated control electrode and a cathode, a direct currentoutput line connected with said valve, a source of negative potential connected with said cathode and with said control electrode, a source of positive potential P connected with said cathode, a capacitor connected across said direct current line to be charged therefrom, an auxiliary valve having an anode connected with the second said source and having a control electrode and a cathode connected with the first said control electrode, means for impressing on the second said control electrode potential of sign and magnitude operative to normally maintain said auxiliary valve conductive, and means for connecting the secdnd said control electrode with said capacitor whereby thesecond said valve is made non-conductiveupon incipient sudden discharge of said capacitor. i

13. In a. system for controlling the flow of electric current, an alternating current supply line, an electric valve connected with said line and having a plurality of anodes'with associated control electrodes and a cathode, a direct current output line connected with said valve, a

capacitor connected across said direct current 60 line to be charged therefrom, a source of negative potential connected with said cathode and with said control electrodes, means connected with said cathode for sequentially impressing on said control'electrodes potential overcoming the potential of the first said source and of sign and magnitude operative to release the flow of current sequentially through said anodes, said means comprising an auxiliary valve having an anode with an associated control electrode and a cathode, means for impressing on the second said control electrode potential of sign and magnitude operative to make said auxiliary valve conductive, and means connecting the second said control electrode with said capacitor whereby the second said valve is made non-conductive upon incipient sudden discharge of said capacitor.

14. In a system of the character described, the combination with an electric current supply circuit, an electric current load circuit, electric valve means interconnecting said circuits and comprising an element for controlling the flow of current therebetween, and a source of current for exciting said element in such sense as to render said means operable for the flow of current between said circuits, of means comprising an electric valve continuously operable during normal operation of said system to connect therethrough said source of current with said element, and means operable responsive to a sudden decrease in the voltage of said load circuit, to control the second said valve in such sense as to interrupt the connection therethrough of said source with said element.

15. In a system of the character described, the combination with an electric current supply circuit, an electric current load circuit, electric valve means interconnecting said circuits and comprising an element for controlling the flow of current therebetween, and a source of current for exciting said element in such sense as to render said means operable for the flow of current between said circuits, of means comprising an auxiliary valve continuously operable during normal operation of said system to connect said source of current with said element, a control electrode for controlling the operation of the second said valve, a source of current for exciting said control electrode in such sense as to interrupt the connection of the first said source with said element by way of the second said valve, and means operable, responsive to a sudden decrease in the voltage of said load circuit, to connect the second said source of current with said electrode. 16. In an electric current converting system, the combination with an electric current supply circuit, an electric current output circuit, and electric valve means comprising an anode and a cathode interconnecting said circuits and constituting spaced electrodes for the flow of current therebetween, of means for controlling said flow of current comprising an element of said valve means, static means responsive to a sudden decrease only in the voltage of said output circuit for impressing on the said element a potential of sign and magnitude operative to cause interrup tion of said flow of current, and means responsive to an abnormal condition of said system for rendering ineffective the third said means.

, crease only in the voltage of current, static 17. In an electric current converting system, the combination with an electric current supply circuit, an electric current output circuit, and electric valve means comprising an anode and a cathode interconnecting said circuits and constituting spaced electrodes for the flow of current therebetween, of means for controlling said flow of current comprising an element of said valve means, static means responsive to a sudden deof said output circuit for impressing on the said element a potential of sign and magnitude operative to cause intereffective the third said means.

18. In an electric current converting system, the combination with an electric current supply circuit, an electric current output circuit, and electric valve means comprising an anode and a cathode interconnecting said circuits and constituting spaced electrodes for the flow of current therebetween, of means for controlling said flow of current comprising an element of said valve means, static means responsive to a sudden decrease only in the voltage of said output circuit for impressing on said element a potential of sign and magnitude operative to cause interruption of said flow of current, and time delay means responsive upon the occurrence of a disturbance in the system to render the third said means momentarily ineffective.

19. In an electric current converting system, the. combination with an electric current supply circuit, an electric current output circuit, and electric valve means comprising an anode and a cathode interconnecting said circuits and constituting spaced electrodes for the flow of electric current therebetween, of means for controlling said flow of current comprising an element of said valve means, means for impressing on said element a potential of such sign and magnitude as to render said valve conductive for said flow means responsive to a sudden decrease only in the voltage of said output circuit for superimposing on said element a potential of such sign and magnitude as to render said valve means non-conductive for said flow of cur rent, and means comprising a time delay relay for rendering the fourth said means momentarily ineiTective.

STEFAN WIDMER. MAX 7 LIMANN. 

